Background
Spanish mackerel is an iconic species that is widely distributed around Australia and targeted by many fisheries. The Spanish mackerel stock on the East Coast of Australia spans both Queensland and New South Wales, with the majority of landings in Queensland. A stock assessment in 2021 indicated this population was depleted and, in response, new management measures were introduced, including a reduction in commercial catch quotas, recreational bag limits, and seasonal closures. Several knowledge gaps were identified during this assessment.
Aims
To improve the robustness of future assessments, a multi-disciplinary research project commenced in 2022 to: 1) investigate the feasibility of Close-Kin-Mark-Recapture (CKMR) for estimating population abundance; 2) quantify shark depredation and post-release mortality; 3) improve the spatial and temporal resolution of fishing effort metrics; and, 4) identify environmental factors influencing recruitment.
Methods and Results
A sample collection program, CKMR design study and population genetic analyses on the East Coast Spanish mackerel stock confirmed the feasibility of CKMR for estimating population abundance, based on the collection of >6,000 tissue samples across Queensland and New South Wales. Data on shark depredation from ~100 commercial, charter and recreational fishing trips, found depredation rates of ~6% in the commercial sector and ~37% in the charter and recreational sector. Thirty-two satellite tags deployed on Spanish mackerel identified a post-release mortality rate of 33%, with shark predation the main cause. A detailed Spanish mackerel fishing effort signature developed for the Queensland fishery has enabled quantification of effort metrics at fine temporal and spatial scales, thereby improving the reliability of catch-per-unit-effort as an index of abundance. Statistical modelling determined that water temperature leading up to the spawning season, rainfall, major flood events and abundance of prey species can significantly affect Spanish mackerel recruitment.
Conclusion
The outputs from this project have made a direct contribution to addressing key data gaps, improving the 2025 stock assessment for Spanish mackerel and increasing our knowledge of the species’ biology and population dynamics. The research has also demonstrated the potential of applying Close-Kin-Mark-Recapture and effort signatures to improve assessment and management of fisheries.